Coating oven



vR. '.x. RUFFA COMING OVEN.

u 5 Sheets-Sheet 1 Filed- April 22, 1958 INVENTOR ATTORNEY E. d. /PaFx-fv lll FIXIII lllllllllllllhlll lllllilllllIJFnUll JIUIIPIIIIIIIII Wm. TQ

Aug. 23, 1960 v R. J. RUFF coATING OVEN 5 Sheets-Sheet 2 Filed April 22, 1958- INVENTOR .my mw ATTORNEY Y R. J. RUFF Aug. 23, 1960 f l, Il l .wm www.

INVENTOR E J /PUFF ATTORNEY coaTrNo ovnN Richard .L Rut?, Detroit, Mich., assigner to Catalytic Combustion Corporation, Detroit, Mich., a corporation of Michigan Filed Apr. 22., 1958, Ser. No. 730,176

1l Claims. (Cl. 265-8) This invention relates to the heat treatment of coated articles or materials and more particularly to an apparatus for heat treating such coated articles or materials to evaporate the solvents or other volatile components in the coatings to dry and bake such coatings on the articles or materials to which they are applied.

The apparatus of this invention may be utilized to heat treat many different types of coatings on many different articles or materials, but is primarily intended to heat treat the printing or other coatings applied to sheet metal materials for decorative or protective purposes and accordingly the invention will be described in connection with the printing or coating of such sheet metal materials or articles, but it is to be understood that this is for illustrative purposes only and that the apparatus is in no way limited to such use.

In the manufacture of containers, such as cotee cans, beer cans, containers for frozen fruit juices, oil cans and other similar containers, decoration is coated and printed on sheet metal plates prior to forming the same into such containers. in some instances, it is necessary to apply a background coating which is baked prior to application of other decorative coatings, some of which may be in varying colors. Certain types of containers, such as beer cans and sardi e cans, have a protective lacquer coating applied to the inside of the container and this is also normally applied to the sheet material prior to formation of the container.

rlhis invention is primarily concerned with an oven for heat treating the coated metal sheet prior to forming the same into containers.

This art has progressed from ovens which would operate at sheet speeds of approximately sixty per minute with a maximum sheet size of approximately twenty-nine by thirty-six inches and in which only approximately ten to tifteen gallons per hour of solvents were liberated or vaporized Whereas present day ovens are capable of operating at speeds of one hundred to one hundred iifty sheets per minute of an approximate size of thirty-four by forty-four inches and where the amount of solvent evaporated during the baking process may be as much as fifty to one hundred twenty gallons per hour. Obviously, this high speed operation places an appreciable load on the oven insofar as heat requirements are concerned and also since the fumes created during operation of an oven of this type are odorous and noxious in character, as well as inliammable, it can well be recognized that the problems in heat treating articles or materials of the type under consideration in order to eliminate prior hazards and also to render the fumes or vapors suitable for discharge to the atmosphere are very considerable. Furthermore, the loads imposed on an oven of this type will vary considerably depending upon the specic type of coating being applied, as well as the speed of operation and consequently ovens which are designed for maximum capacity may very well operate at an extremely low efliciency when running at less than maximum capacity. This factor is of a particular importance in connection with Patented 233, l@

the supply of fresh air provided to the oven for diluting the vaporized solvents to a suticient extent to prevent any danger of re and at the same time, prevent condensation of the vaporized solvents which would result in creating a hre hazard and also requiring frequent cleaning of the oven and associated equipment. Fire insurance underwriters specify certain standards for ventilation of ovens by utilizing an explosimeter which operates to vary the supply of fresh air in accordance with the solvent load on the oven and While such systems have been utilized with the vtacit approval of the insurance underwriters, nevertheless, it is considered that the practice is somewhat dangerous in that, there is an appreciable time lag in operation of the system and it may be entirely possible that upon the imposition of a sudden full solvent load on the oven, that the system will not sense the change in time to increase the supply of fresh air sufficiently to maintain conditions in which no re hazard is present.

Furthermore, with prior ovens of the type under consideration there has always been the problem of infiltration air at the entrance end of the oven and heretofore this air has been allowed to mix indiscriminately with the vaporized solvent in the iirst portion of the oven which resulted in materially increasing the heat input requirements and also this inltration air was introduced in such y a way that it could not be considered as part of the fresh air utilized to ventilate the system and dilute the vapors to a point where fire hazard ceased to exist. Accordingly, an oven of the type under consideration which is designed to treat the vaporized solvents in such a manner that the oven may be exhausted to the atmosphere without undue polution of the same and also an oven in which the infiltrated fresh air at the entrance end of the oven may be utilized as part of the Ventilating or diluting air and without materially increasing the input requirements of the oven represents a very material step for- Ward in the art. It will, therefore, be seen that it is extremely desirable to provide a heat treating apparatus of the character under consideration which will eliminate all discharge of vapor or fume laden air and furthermore, since the fumes or vapors from the solvents of the coatings may be oxidized through catalytic action, the heat available from such oxidation can be utilized and will normally be adequate to supply the total heat requirement of the oven and the apparatus of the instant invention is designed to accomplish this result.

It is accordingly an object of the invention to provide a coating oven for heat treating coated articles or materials to evaporate coating solvents and in which one or more catalytic vapor incinerators may be utilized to oxidize the combustibles in the vaporized solvents to thereby remove noxious fumes and at the same time, provide all or part of the heat necessary to operate the oven.

A further object of the invention is the provision of a coating oven for heat treating coated articles or materials to evaporate coating solvents and remove combustibles therefrom in which the coated articles or materials are Autilized to supply heat for operating the oven and in 3 which all noxious fumes are removed from the vaporized solvents to permit exhaust to the atmosphere.

A still further object of the invention is the provision of a coating oven for heat treated coated articles or materials to evaporate coatingvsolvents and remove combustibles from the vaporized solvents-and including an elongated heat treating chamber having a plurality of heat treating zones, the vaporized solvents from the first zone being directed through a heating burner and a catalytic vapor incinerator and including means for permitting a portion of the vaporized solvents to by-pass the burners and incinerator.

Another object of the invention is the provision of aV coating oven for heat treating coated articles to evaporate coating solvents and remove combustibles from thevaporized solvents including an elongated heat treating chamber having a plurality of heat treating zones with the vaporized solvents in the rst zone being directed through heating burners and a catalytic vapor incinerator and including means for bypassing iniiltration fresh air at the entrance end of the first zone by the burners and incinerator to prevent dilution of the vaporized solvents prior to treatment by the incinerator.

A further object of the invention is the provision of a coating oven for heat treating coatedsarticles to evaporate coating solvents and remove combustibles from the vaporized solvents including an elongated heat treating oven having a plurality of heat treating zones, the vaporized solvents from the rst and second zones being treated by catalytic vapor incnerators with the exhaust yfrom the incinerator for the second zone being directed through a plurality of heat exchangers to provide heat -for treating articles in the zones'following the second zone, aslwell as in the second zone.

A still further object of the invention is the provision of a coating oven for heat treating coated articles to evaporate coated solvents and remove combustibles from the vaporized solvents including an elongated heat treating chamber having a plurality of heat treating zones and in which catalytic vapor incinerators areutilized to remove the combustibles from the vaporized solvents, the exhaust from onerrincinerator being directed through a plurality of heat exchangers and re-circulating fans for certain of the zones connected to the heat exchangers for circulatingl heated air through the zones and exchangers, together with means for Vcontrolling proportion ately the air passing through the exchanger and being by-passed direct to the faninlet.

Another object ofthe invention is the provision of a coating oven for heat treating coated articles to evapou rate coating solvents and remove-combustibles from the vaporized solvents including. an elongated heat treating chamber having a plurality of heat treating zones and in which means is provided for introducing fresh yair to the iirst zone and also for introducing freshvair to the last zone.

A further obiect of thevinvent-ionis the provision of a-coating oven for heat treating coated articles to evaporate coating solvents and'remove-combustibles from the vaporized solvents, including an elongated heat treating chamber and an endless conveyor to convey articles or materials through the chamber, together with means for pre-heating the conveyor prior to the feeding of articles thereto and introduction of such articles into the treating chamber, the heat for pre-heating such conveyor being obtained from one of the heat treating zones in the heat treating chamber.

Further objects and advantages of the invention-will" be apparent from the following descriptionftaken-in con-` junction with the accompanying drawings wherein:

Fig.V la is a Side elevational view of a lcoating ovenconstructed in accordance with this invention;

Fig. 1b a side elevational view constituting a continuation of Fig. la andshowing the remainder. of the heat shown in Fig. 1b;

Fig. 3 a sectional view taken substantially on the line 3 3 of Fig. la and showing the arrangement of the inltration air by-pass ducts at the entrance to the heat treating chamber and the iirst heat treating zone;

Fig. 4 a sectional view taken substantially on the line 4 4 of Fig. 2a and showing the arrangement of one of the heat exchangers, circulating fan and associated heat treating zone;

Fig. 5 a fragmentary sectional view taken Substantially on the line 5 5 of Fig. 2b and showing the structure of one of the heat exchangers, as well as the relationship of the air passages and the inlet to the circulating fan for the associated heat treating chamber;

Fig. 6 a sectional view taken substantially on the line 6 6 of Fig. 2b and showing a damper arrangement for controlling the flow of air over the surfaces of the heat exchanger, as well as for by-passing air directly to the inlet of the circulating fan and also showing the fresh air inlet for the last treating zone of the apparatus;

Fig. 7 a top plan view showing the manner in which a conveyor pre-heater, as Well as the heat supply for such pre-heater may beincorporated in the coating oven of this invention;

Fig. 8 a fragmentary side elevational view of the apparatus shown in Fig. 7 and showing the arrangement of the conveyor pre-heating system; and

Fig. 9 a sectional view taken substantially on the line 9 9 of Fig. 8 and showing the conveyor pre-heating chamber, as well as the manner of supplying heated air thereto and returning air from the pre-heating cham- `ber to be re-heated and re-circulated.

With continued reference to the drawing, there is shown a coating oven constructed inaccordance with this invention and which may well comprise an elongated housing lt composed of a top wall ii, sidewalls l2 and i3 and a bottom wall provided by a supporting surface 14, such as the oor of a building or other surface. Of course, if desired, a separate bottom wall may be provided and lform an integral part of the housing lil. Also provided in the housing 1i) is a longi tudinally extending partition 15 and a second longitudinally extending partition 16 disposed below the partition i5 and providing an elongated heat treating chamber 17. An endless conveyor 18 having wickets i9 or other suitable means thereon for receiving and support ing sheets cr articles to be treated is mounted to pass through the chamber i7 on suitable trackways or the like 20 and the lower flight of the conveyor i8 passes through a chamber 21 below the partition 16 and may be supported on suitable trackways or the like 22. The conveyor 18 may be mounted adjacent the ends of the heat treating chamber i7 on pulleys or other suitable means 18.

The heat treating chamber 17 may be divided into a first heat treating zone 23, a second heat treating zone 24, subsequent heat treating zones 25 and a last heat treating zone 26. Only one subsequent heat treating zone 25 is shown in the drawing for the purpose of sirnplicity, but it is to be understood, that any' number of such zones which are considered necessary may be incorporated between the second heat treating zone 2,4- and the last heat treating zone 25. Since the structure of any additional subsequent heat treating zones Will be identical with the zone 2.5 it is considered that a descripl tion of the structure of zone 2S is all that is necessary to provide an accurate understanding of the structure and operation of the invention.

A plenum chamber 27 may be disposed below the cont veyor 1S in the rst zone 23 in order to direct heated gases through the articles or materials carried by the conveyor 18 and a vapor exhaust duct 28 may be provided above the first zone 23 for conducting Vaporized solvents therefrom. Disposed in the exhaust duct 28 are heating burners 29 to which gas or other fuel may be supplied and also disposed in the exhaust duct following the burners 29 is a catalytic vapor incinerator 30. The catalytic vapor or fume incinerator 30 may be of the type disclosed in patent to Suter et al., No, 2,658,742, dated November 10, 1953, or may be of any' other suitable type and no detailed description of this incinerator is believed necessary or desirable, reference being made to the above patent for this purpose. Since the incinerator 30 is located directly in the iiow of vapor or fume laden air from the burners 29' there is no dilution thereof prior to contact with the catalyst and consequently, such catalyst may operate at peak efficiency. A circulating fan 31 is provided with an inlet 32 connected to the duct 28 following the incinerator 30 and the outlet 33 of the circulating fan 31 is connected to the plenum chamber 27. It will thus be seen, that gases heated by the burners 29 and by the catalytic incinerator 30 will pass to the inlet 32 of the fan 31 and thereafter be re-circulated through the plenum chamber 27 and the first heat treating Zone 23.

Since a certain amount of fresh air will infiltrate into the first heat treating zone 23 through the entrance end thereof because the same cannot be sealed, it is desirable to prevent direct mixing of such infiltrated air with the vapor laden fumes in the first treating zone 23, because dilution of such air prior to passing through the catalytic incinerator 30 is undesirable. Consequently, infiltration air conduits 34 and 35 are provided on each side of the entrance end of the heat treating zone 23 and such conduits connect with a common conduit 36 which by-passes the burners 29 and catalytic incinerator 30 and discharges directly into the duct 28 between the incinerator 30 and the inlet 32 of the fan 31. Consequently, infiltrated air will be collected in the by-pass ducts 34 and 35 and will be discharged through the inlet of the fan 31 and mixed with the air flowing from the incinerator 30 to be re-circulated through the plenum chamber 27 and rst treating zone 23.

When first starting the coating oven of this invention, the fume or vapor laden air passing from the first treating Zone 23 will be heated by the burners 29 to a sufcient temperature to activate the catalytic incinerator 30, but thereafter, depending upon the quanttiy of solvents present in the air flowing thereto, the incinerator 30 will provide all of the heat necessary to treat the articles passing through the first treating Zone 23 and consequently, the flow of fuel to the burners 29 may be reduced by suitable control means thereby reducing the cost of operation of the apparatus.`

Since it is sometimes desirable to introduce addition-al fresh air to the rst treating zone 23, for this purpose there may be provided a fresh air inlet 37 communicating with the duct 28 between the incinerator 30 and the inlet 32 of the fan 31 and a suitable damper 39 may be provided for controlling the iiow of fresh air through the inlet 37.

Since it is also sometimes desirable to by-pass a portion of the fume or solvent laden air by the burners 29 and incinerator 30, there may be provided a vapor passage 40 between the first treating zone 23 and the duct 28 between the incinerator 30 and the inlet 32 of the fan 31 and this passage 40 may be controlled by suitable dampers o rother means 41 which may be automatically 43 may be disposed above the second zone 24 and a portion ofthe first zone 23. A vapor exhaust duct 44 is connected to the hood 43 and to the inlet 45 of a blow* er 46 with the outlet 47 of the blower 46 being connected to a conduit 48 disposed above the heat treating chamber 17 and in which may be located a series of heat exchangers 49, 50 and 51. It is to be noted, that heat exchanger 49v is located adjacent the second heat treating zone 24, heat exchanger 50 adjacent the subsequent heat treating zone 25 and heat exchanger 51 adjacent the last heat treating zone 26. The heated gases after passing through the last heat exchanger 51 are discharged to the atmosphere through a suitable stack or other means 52.

Disposed in the conduit 48 between the blower 46 and the first heat exchanger 49 is a heating burner 53 and disposed in the conduit 48 between the burner 53 and the rst heat exchanger 49 is a second catalytic vapor or fume incinerator 54. Consequently it will be seen that gases passing from the second heat treating zone 24 and also from the first heat treating zone 23 will be drawn into the hood 43 and through the exhaust duct 44 into the inlet 45 of the blower 46 and thereafter through the heating burners 53 and incinerator 54 to be forced through the heat exchangers 49, 50 and 51 to the stack 52 The gases passing from the second incinerator 54 throughthe heat exchangers 49, 50 and 51 will supply heat for treating the articles in the second zone 24, as well as the subsequent zone 25 and last zone 26 and for this purpose there may be provided a circulating fan 55 having an inlet 56 connected to the heat exchanger 49 and an outlet 57 connected to the second plenum chamber 42. A second hood 57 may be disposed above the second treating zone 24 and gases passing from such zone will be collected by the hood 57 which communicates through an opening 58 with the heat exchanger 49 and consequently, such gases Will pass through the heat exchanger 49 and through the inlet 56 into the fan 55 to be re-circulated through the plenum chamber 42 and the second heat treating zone 24.

In a similar manner, a plenum chamber 59 may be disposed below the subsequent heat treating zone 25 and a hood 60 may be disposed above such Zone and communicate through an opening 61 with the heat exchanger 56 which in turn is connected through an inlet 62 with a circulating fan 63, the outlet 64 of which is connected to the plenum chamber 59. Consequently operation of the fan 63 will result in circulating air heated by the heat exchanger 50 through the plenum chamber 59 and the subsequent heat treating zone 25.

A last plenum chamber 65 may be disposed below the last heat treating zone 26 and a hood 66 may be provided Vabove the heat treating zone 26 and communicate through an opening 67 with the last heat exchanger 51 which in turn is connected to the inlet 68 of a circulating fan 69, the outlet '76 of which is connected to the plenum chamber 65. Consequently, operation of the fan 69 will serve to circulate air heated by the last heat exchanger 51 through the plenum chamber 65 and the last heat treating zone 26.

Since it is desir-able to provide fresh air for the last heat treating zone 26, there may be provided a fresh air inlet 71 connected to the last heat exchanger 51 and a suitable damper or other control means 72 may be provided in the fresh air inlet 71 to control the amount of air introduced therethrough to the last heat exchanger 51 and the treating zone 26.

`It will thus be seen that the heat necessary for treating the articles and materials in the first and second zones 23 and 24 may be provided in the first instance, by the burners 29 and 53 and thereafter by the catalytic incinerators 30 and 54 and also that the entire heat requirements of the subsequent zones 25 and last zone 26, as well as the requirements of the second zone 24 may be provided by the incinerator 54 in conjunction with the heat exchangers 49, 50 and 51. Also the fresh airintroduced into-'the' heattreating chamber 117'` through the fresh air inlet V"llimay be-controlled as-fdesired, as wellasfany fresh air which may beintroduced through'th'e inlet 37 and, furthermore, inltrating fresh airirom-theentranee end ofthe treating chamber -17 will 'notoperate to dilute the vaporsor vfumes passing `through the tirstcatalytic incinerator 3d, but will be Vintroduced into fthe zaini-:low thereafter andsuch inltrated Avairirnay, consequently, libe considered as apart of thefre'sh air introduced intofthe system to maintain solvent concentrationat such -alpoint that no fire hazard exists. Furthermore, the 'inltrated air at the entranceend of the oven doesnot-operate to cool the vapor or fume laden air and consequently, condensation is reduced to aminimum `with'the'-result'tthat lire hazard is"reduced and also'thenecessity for frequent cleaning ofthe'app'aratus.

The heat 'exchangers 49, 50 and V51`for convenience are shown as conventional tubular heat'exchangers,`but it is to be understood that this is'for illustrative purposes only and that any `suitable "type bf 'heat exchanger may be employed and'thatthe Vprinciple 'of operation will be the same in any case.

Since it is"`fre`quently desirable -to control the 'tempera- Y ture in individualtreatingzones, there maybeprovided means for such control whichds particularly shown in Fig. 6 and, ofcourse, such. means 4may b'eincorporat'ed'in any or all of the heat treating zones. As'sh'own in Fig. 6, there maybe provided a suitable bathe 73'for 'dividing the flow of gas from thetreating chamber 17 with the how in one direction passing through the 'associated'heat exchanger and withflow inthe opposite direction passing directly to the inlet68 of the circulating 'fan 69. In order to control the/flow of gas through the heat exchanger 51 or directly to the inlet 68 of 'the fan 69, there may be provided a system of dampers'74 and 75 which may be manually actuated or Vactuated by a proportionate controller in order to direct ythe gas iiowing from the treating chamber 17, either to'theheat exchanger `51 or tothe inlet 68 of the fan 69 or the dampers 74 and75 'may be so controlled that part of the gaswillpass through the heat exchanger 51 and part directlyto the inlet 68 of the fan 69. In this manner, the temperature ineach 'of the treating zones may be conveniently controlled.

Since the conveyor'iS absorbs a signiiicant portion of the heat input to the oven of this invention Vand since the lower night of vsu'chcouveyor passes through a relatively cool atmosphere,'it`may well be found desirableto pre heat such conveyor in order to minimize cooling of the articles or materials deposited on the conveyor and Aalso to maintain the efliciency of the oven at a higher point. With particular reference to Figs. 7, 8 and 9, there ris shown a structure for pre-heating the conveyor 18 and whichmay well comprise a pre-heating chamber 76 disposed below the heat treating chamber 17 and through which the lower flight of the conveyor 18 passes. A circulating fan 77 may have an inlet '78 connected tothe conduit 48 between the second incinerator 54 and the first heat exchanger 49 `and the inlet'TS may if desired, be controlled by suitable dampers or other means 79. The outlet of the fan 77 is connected to the pre-heating chamber 76 and will supply heated'air thereto to properly pre-heat the conveyor`18. In order that the air supplied to the pre-heating chamber 76 may be re-circulated a return duct 8i may be connected at 32 to the pre-heating chamber 76 and an outlet 83 Vof the return duct 81 may be connected to the inlet 78 of the circulating fan 77. Thus with the dampers 79 closed the air is recirculated'or the dampers 79 may be adjusted to mix air,from the conduit 4S with the recirculated air.

It will thus be seen that 'by the above described invention there has been provided an oven for suitably heat treating coatedarticlestoevaporate coatingsolvents and remove combustibles therefromfand in which catalytic vapor or .tumeincinerators are utilized to remove such combustibles and lalso at the same time, to provide heat for operating theoven. Furthermore, the infiltration of fresh 'air-fat :th'eentrance end of the oven is divertedand dire'ctedin su'chia manner, that the same will not operate to Cause undue condensation or dilution of vapor or .fume laden air with the result that the oven operates at a higher efficiency lthan would be the case if the infiltrated air mixed directly with the vapor or fume laden air in the treating chamber and-also adequate control is provided to control thetemperature throughout the treating process and also to pre-heatthe conveyor .utilized to convey articles or materialsthrough the treating chamber in order to .maintain such eiciency at. a maximum.

ltwi-llbeobviousto.those'skilled in the art that various changesimay `bemade inthe invention without 'departing from thespiritfan'd scope thereof and thereforethe invention is-.no't limitedby that which is shown in Vthe-drawings 'and described in'the specification, 'but only 1as indicated in theappende'dfclaims `Y'Vhat'is claimedis:

l. `A coating oven for heat treating coated articles to evaporate coating solvents and remove combustibles from tht vaporized solvents, said oven comprising an elongated heat treating chamber, -having an entrance at one end andan exit 'at the other, an endless conveyor for conveying coated articles to be heated through said chamber from the entrance end to the exit end, a conveyor preheating chamber below said heat treating chamber, means for supplying heatvto said Ypre-htating chamber, a plurality -of'heat treating zones spaced longitudinally of said hettreating chamber including a irst zone adjacent sid entrance end, a second zone following said rst zone, subsequent zones following said second zone with a lastzone adjacent said exitendfa plenum chamber disposedbelow said Vconveyor in said first zone Vfor directing heated gases over coated `articles carried by said conveyor, an open `vapor exhaust duct in said lfirst zone spacedinwardly of said'entrance end, heating burners in said duct for heating gases passing -therethrough from said v iirs't zone, a catalytic vapor incinerator disposed in said duct following said burners, a circulating fan having an inlet connected to said duct foliowing said incinerator and an outlet connected to said plenum chamber, an inltration air by-pass conduit having an inlet opening adjacent the V'entrance end of said heat'treating chamber'anda Vdischarge opening'into said duct between said incinerator andthe inlet to said fan, a damper controlled fresh air inlet connected to said duct between said incinerator and said fan inlet, 'a dmnper'controlled vapor passage connecting said first 'zone and said duct between said incinerator and said fan inlet, aseeond plenum chamber 'disposed below saidconveyor in said second zone for vdirecting heated gases .over the coated articles carriedby said conveyor, a vapor collecting hood disposed oversaid second zone and arportion or" said first zone, a `second open vapor txhaust duct connected to'said hood,.a.series of heatexchangers, a blower having an inlet connected to said second exhaust duct and an outlet connected tov said series of heat exchangers adjacent said second zone, said subsequent zones and said last zone andl discharging to the atmosphere, heating burners disposed in said last named outlet between -said blower and the tirst heat exchanger, a second catalytic vapor incinerator disposed in said last named outlet between saidiast Ynamed burners andthe rst heat exchanger,.a second hood disposed above said second zone and connected to the rst heat exchanger, a second circulating fan having an'inlet connected to the tirst heat exchanger and `an 'outlet connected to said second plesaid subsequent and last zones, circulating fans for said subsequent and last Zones having inlets connected to the heat exchangers adjacent said subsequent and last zones and outlets connected to the plenum chambers in said subsequent and last zones, a damper controlled fresh air inlet connected to the heat exchanger adjacent said last zone and damper controlled means associated with said second hood, said subsequent hoods and said last hood for proportionately directing air flow from the associated hood through the associated heat exchanger and directly to the inlet of the associated circulating 2. A coating oven for heat treating coated articles to evaporate coating solvents and remove combustibles from the vaporized solvents, said oven comprising an elongated heat treating chamber, having an entrance at one end and an exit at the other, an endless conveyor Yfor conveying coated articles to be heat treated through chamber from the entrance end -to the exit end, a plurality of heat treating zones spaced longitudinally of said heat treating chamber including a first zone adjacent said entrance end, a second zone following said first zone, subsequent zones following said second zone with a last zone adjacent said exit end, a plenum chamber disposed below said conveyor in said first zone for directing heated gases over coated articles carried by said conveyor, an open vapor exhaust duct in said rst zone spaced inwardiy of said entrance end, heating burners in said duct for heating gases passing therethrough from said first Zone, a catalytic vapor incinera-tor disposed in said duct following said burners, a circulating fan having an inlet connected to said duct following said incinerator and an outlet connected to said plenum chamber, an infiltration air by-pass conduit having an inlet opening adjacent the entrance end of said heat treating chamber and a discharge opening into said duct between said incinerator and the inlet to said fan, a damper controlled fresh air inlet connected to said duct between said incinerator and said fan inlet, a damper controlled vapor passage connecting said first zone and said duct between said incinerator and said fan inlet, a second plenum chamber disposed below said conveyor in said second zone for directing heated gases over coated articles carried by said conveyor, a vapor collecting hood disposed above said second zone and a portion of said first Zone, a second open vapor exhaust duct connected to said hood, a series of heat exchangers, a blower having an inlet connected to said second exhaust duct and an outlet connected to said series of heat exchangers adjacent said second Zone, said subsequent zones and said last zone and discharging to the atmosphere, heating burners disposed in said last named outlet between said blower and the first heat exchanger, a second catalytic vapor incinerator disposed in said last named outlet between said last named burners and the first heat exchanger, a second hood disposed above said second zone and connected to the first heat exchanger, a second circulating fan having an inlet connected to the first heat exchanger and an outlet connected to said second plenum chamber, subsequent plenum chambers disposed below said conveyor in said subsequent zones and a last plenum chamber disposed below said conveyor in said last zone, subsequent hoods disposed above said subsequent zones and a last hood disposed above said last zone, said subsequent and last hoods being connected to the heat exchangers adjacent said subsequent and last zones, circulating fans for said subsequent and last zones having inlets connected to the heat exchangers adjacent said subsequent and last Zones and outlet connected to the plenum chambers in said subsequent and last zones, a damper controlled fresh air inlet connected to the heat exchanger adjacent said last zone and damper control means associated with said second hood, said subsequent hoods and said last hood for proportionately directing air flow from the associated hood through the associated heat exchanger and directly to the inlet of the associated circulating fan.

3. A coating oven for heat treating coated articlesV to evaporate coating solvents and remove combustibles from the vaporized solvents, said oven comprising an elongated heatrtreating chamber having an entrance at one end and an exit at the other, an endless conveyor for conveying coated articles to be heat treated through said chamber from the entrance end to the exit end, a plurality of heat treating zones spaced longitudinally of said heat treating chamber including a first zone adjacent said entrance end, a second zone following said first zone, subsequent zones following said second zone with a last zone adjacent said exit end, a plenum chamber disposed below said conveyor in said first zone for directing heated gases over coated articles carried by said conveyor, an

open vapor exhaust duct in said rst Zone spaced inwardly of said entrance end, heating burners in said duct for heating gases passing therethrough from said first zone, a catalytic vapor incinerator disposed in said duct following said burners, a circulating fan having an inlet connected to said duct following said incinerator and an outlet connected to said plenum chamber, an infiltration air by-pass conduit having an inlet opening adjacent the entrance end of said heat treating chamber and a discharge opening into said duct between said incinerator and the inlet to said fan, a damper controlled fresh air inlet connected to said duct between said incinerator and said fan inlet, a damper controlled vapor passage connecting said rst zone and said duet between said incinerator and said fan inlet, a second plenum chamber disposed below said conveyor in said second zone for directing heated gases over coated articles as carried by said conveyor, a second open vapor exhaust duct communicating with said second Zone, a series of heat exchangers, akblower having an inlet connected to said second exhaust duct and an outlet connected to said series of said heat exchangers adjacent said second zone, said subsequent zones and said last zone and discharging to the atmosphere, heating burners disposed in said last named outlet between said blower and the first heat exchanger, a second catalytic vapor incinerator disposed in said last named outlet between said last named burners and the rst heat exchanger, a second hood disposed above said second zone and connected to the first heat exchanger, a second circulating fan having an inlet connected to the first heat exchanger and an outlet connected to said second plenum chamber, subsequent plenum chambers disposed below said conveyor in said subsequent zones and a last plenum chamber disposed below said conveyor in said last zone, subsequent hoods disposed above said subsequent zones and a last hood disposed above said last zone, said subsequent and last hoods being connected with the heat exchangers adjacent said subsequent and last zones, circulating fans for said subsequent and last zones having inlets connected t0 the heat exchangers adjacent said subsequent and last zones and outlets connected to the plenum chambers connected to said subsequent and last zones, a damper controlled fresh air inlet connected to the heat exchangerv adjacent said last zone and damper control means associated with said second exhaust duct, said subsequent hoods and said last hood for proportionately directing air flow from the associated hood through the associated heat exchanger and directly to the inlet of the associated circulating fan.

4. A coating oven for heat treating coated articles to evaporate coating solvents and remove combustibles from the vaporized solvents, said oven comprising an elongated heat treating chamber having an entrance at one end and an exit at the other, an endless conveyor for conveying coated articles to be heat treated through said chamber from the entrance end to the exit end, a plurality of heat treating zones spaced longitudinally of said heat treating chamber including a rst zone adjacent said entrance end, a second zone following said rst Zone, subsequent zones following said second zones with a last zone adjacent said exit ends, a plenum chamber disposed below said conveyor in said first Zone for directing heated gases over coated articles carried by saidconveyor, -an open vapor exhaust duct in said first zone spaced inwardly of said entrance-end, heating burners in said duct for heating gases passing therethrough .from said :first zone, a catalytic vapor incinerator disposed in said duct following said burners, a circulating fanhaving aninlet connected to said duct following vsaid incinerator and an outlet connected to said plenum chamber, aninfiltration air by-pass conduit having aninlet opening adjacent the entrance end of said heat treating chamber and a discharge opening into saidduct betweenfsaid incinerator and the inlet to said fan, a damper controlled fresh air inlet connected to said duct between said'incinerator and said fan inlet connected to said duct between said incinerator and said fan inlet, a damper controlled vapor passage connecting said first zone and saidduct between said incinerator and said fan inlet, a second plenum chamber disposed below said conveyor in vsaid second zone by directing heated gases over coated articles carried by-said conveyor, a second open vapor exhaust duct communicating with said second zone, a series of heat exchangers, a blower having an inlet `connected to said second exhaust duct and an outlet connected-to said series of heat exchangers adjacent said secondzone, said subsequent zones and said last zone and dischargingto the atmosphere heating burners disposed in said last named outlet between said blower and the first heat exchanger, a second catalytic 'vapor incinerator disposed in said last named outlet between said last named burners and the first heat exchanger, a third duct connecting said second zone and the first heat exchanger, a second `circulating fan having an inlet connected to the rst heat exchanger and an outlet connected to said second plenum chamber, subsequent plenum chambers disposed below said conveyor in said subsequent zone and a Vlast plenum chamber disposed below said conveyor in said last zone, said subsequent and last zones being connected through subsequent and last ducts to the heat exchangers adjacent said subsequent and last Zones, circulating fans for said subsequent and last zones having inlets connected to the inlets adjacent said subsequent and last zones and outlets connected to the plenum chambers .in said subsequent and last zones, a damper'controlledrfresh air-inlet connectedto -the heat exchanger adjacent-said last zone and damper control means associated with said second exhaust duct, saidthird duct and said-subsequent and last ducts Vfor proportionately directing-air flow from the associated heat exchanger Yand directly tothe inlet of the associated circulating fan.

A coating oven for heattreating coated articlesto evaporate coating solvents and remove combustibles-from the vaporized solvents, said Voven comprising an'eiongated heat treating chamberhaving an entrance at one' end and an exit at the other, an Vendless conveyor for conveying coated articles'to be'heattreated through said chamber from theentrance endvto'the'exit end,fa plurality of heat treating zones spaced longitudinally of'said heat treating chamber including a first zone 'adjacent said entrance end, a second zone followingsaid first zone, subsequent,Zones'following said second Vzone with alas't zone adjacent saidexit end, agplenurnchamber disposed below said conveyor in said first zone for directing heated gases over coated articles carriedfbysaid conveyor, .an open vapor exhaust duct in said first'zone spaced inwardly of said entrance end, heating burners in said duct for heating gases passing therethrough-'from -said first Zone, a catalytic vapor-incinerator disposed in said ductfollowing said burners, la circulating fan-having an inlet connected to said-duct followingfsaid incinerator and an outlet connectedto 'saidl plenum chamber, an infiltration air oy-pass conduit havingfan inlet `opening adjacent the-entrancelend of said heat treating chamber and a discharge opening into `saidduct between said incinerator and the inlet to said fan, a damper controlled fresh air inlet connected to said duct between said incinerator and said fan inlet, a damper controlled vapor passage connecting said first Zone and said duct between said incinerator and said fan inlet, a second plenum chamber disposed below said conveyor in said second zone for directing heated gases over coated articles carried by said conveyor, a second open exhaust duct communicating with said second zone, a series of heat exchangers, a blower having an inlet connected to said second exhaust duct and an `outlet connected to a said series of heat exchangers adjacent said second zone, said subsequent zones and said last zone and discharging to the atmosphere, heating burners disposed in said last named outlet between said blower and the first heat exchanger, a second catalytic vapor incinerator disposed in said last named outlet between said last named burners and the first heat exchanger, a third duct connecting said second zone and the first heat exchanger, a second circulating fan having an inlet connected to the first heat exchanger and an outlet connected to said second plenum chamber, subsequent plenum chambers disposed below said conveyor in said subsequent zones ,and said last plenum chamber disposed below said conveyor in said last zone, said subsequent and Zlast Zones being connected through subsequent and last ducts to the heat exchangers adjacent said subsequent and last zones, circulating fans for said subsequent and last zones having inlets connected to the heat exchangers adjacent said subsequent and last zones and outlets connected to the plenum chambers in said subsequent and last zones and a damper controlled fresh air inlet connected to rthe heat exchanger adjacent said last zone.

6. A coating oven for heat treating coated articles to evaporate coating solvents and remove combustibles from the vaporized solvents, said oven comprising an elongated heat treating chamber having an entrance at one end and an exit at the other, means for conveying coated articles to be heat treated through said chamber from the entrance end to the exit end, a plurality of heat treating zones spaced longitudinally of said heat treating chamber including a first Zone adjacent said entrance end, a second zone following said first zone, subsequent zones following said second zone with a last zone adjacent said exit end, a plenum chamber disposed below said first zone for directing heated gases over coated articles, an open vapor exhaust duct in said first zone spaced inwardly of said entrance end, heating burners in said duct for heating gases passing therethrough for said first zone, a catalytic vapor incinerator disposed in said duct following said burners, a circulating fan having an inlet connected to said duct following said incinerator and an outlet connected to said plenum chamber, an infiltration air by-pass conduit having an inlet opening adjacent the entrance end of said heat treating chamber and -a discharge opening into said duct between said incinerator and the inlet to said fan, a damper controlled fresh air inlet connected to said duct betweensaid incinerator and said fan inlet, a damper controlled vapor passage connecting sai'd first Zone and said duct between said incinerator and said fan inlet, a second plenum chamber disposed below said second Zone for directing heated gases over coated articles, a vsecond open vapor exhaust duct communicating with said second zone, a series of heat exchangers, a blowerhaving an inlet connected to said second exhaust duct and an outlet connected to said series of heat exchanges adjacent said second zone, said subsequent zones and said last Zone and discharging to the atmosphere, heating burners disposed in said last named outlet between said blower and the first heat exchanger, a second catalytic vapor incinerator disposed in said last named outlet between said last named burners and `said first heat exchanger, a third duct connecting said second zone and the first heat exchanger, a second circulating fan having an inlet connected to the first heat exchanger and an outlet connected to said second plenum chamber, subsequent plenum chambers disposed below said subsequent Zones and a last plenum chamber disposed below said last zone, said subsequent and last zones being connected through subsequent and last ducts to the heat exchangers adjacent said subsequent and last zones, circulating fans for said subsequent and last zones having inlets connected to the heat exchangers adjacent said subsequent and last zones and outlets connected to the plenum chambers in said subsequent and last zones and a damper controlled fresh air inlet connected -to the heat exchanger adjacent said last zone.

7. A coating oven for heat treatingcoated articles to evaporate coating solvents and remove combustibles from the vaporized solvents, said oven comprising an elongated heat treating chamber having an entrance at one end and an exit at the other, means for conveying coated articles to be heat treated through said chamber from the entrance end to the exit end, a plurality of heat treating zones spaced longitudinally of said heat treating chamber including a first zone adjacent said entrance end, a second zone following said first zone, subsequent zones following said second zone with said last zone adjacent said exit end, aplenum chamber communicating with said rst zone for directing heated gases over coated articles, an open vapor exhaust duct in said first zone spaced inwardly of said entrance end, heating burners in said duct for heating gases passing therethrough from said first zone, a catalytic vapor incinerator disposed in said duct following said burners, a circulating fan having an inlet connected to said duct following said incinerator and an outlet connected to said plenum chamber, an infiltration air by-pass conduit having an inlet opening adjacent the entrance end of said heat treating chamber and a discharge opening into said duct between said incinerator and the inlet to said fan, a damper controlled fresh air inlet connected to said duct between said incinerator and said fan inlet, a damper controlled vapor passage connecting said first zone and said duct between said incinerator and said fan inlet, a second plenum chamber communicating with said second zone for directing heated gases over coated articles, a second open vapor exhaust duct communicating with said second zone, a series of heat exchangers, a blower having an inlet connecting with said second exhaust duct and an outlet connected to said series of heat exchangers adjacent said second Zone, said second zones and said last zone and discharging to the atmosphere, heating burners disposed in said last named outlet between said blower and the first heat exchanger, a second catalytic vapor incinerator disposed in said last named outletv between said last named burners and the rst heat ex changer, a third duct connecting said second zonejand;

the first heat exchanger, a second circulating fan having an inlet connected to the first heat exchanger and an outlet connected to said second plenum chamber, subsequent plenum chambers communicating with said subsequent zones, and a last plenum chamber communicating with said last zone, said subsequent and last zones being connected to subsequent and last ducts to the heat exchangers adjacent said subsequent and last zones, circulating fans for said subsequent and last zones having inlets connected to the heat exchangers adjacent said subsequent and last zones and outlets connected to the plenum chambers in said subsequent and last zones and a damper controlled fresh air inlet connected to the heat exchanger adjacent said last zone.

8. A coating oven for heat treating coated articles to evaporate coating solvents and remove combustibles from the vaporized solvents, said oven comprising an elongated heat treating chamber having an entrance at one end and an exit at the other, means for conveying coated articles to be heat treated through said chamber from the entrance end to the exit end, a plurality of heat 14 treating zones spaced longitudinally of said heat treating chamber including a first zone adjacent said entrance end, a second zone following said first zone, subsequent zones following said second zone with a last zone adjacent said exit end, a plenum chamber communicating with said first zone for directing heated gases over coated articles, an open vapor exhaust duct in said first zone spaced inwardly of saidentrance end, heating burners in said ducts for heating gases passing therethrough from said first zone, a catalytic vapor incinerator disposed in said duct following said burners, a circulating fan having an inlet connected to said duct following said incinerator and an outlet connected to said plenum chamber, an infiltration air by-pass conduit having an inlet opening adjacent the entrance end of said heat treating chamber and a discharge opening into said duct between said incinerator and the inlet to said fan, a damper controlledvapor passage connecting said first zone and said duct between said incinerator and said fan inlet, a second plenum chamber communicating with said second zone for directing heated gases over coated articles, a second open vapor exhaust duct communicating with said second zone, a series of heat exchangers, a blower having an inlet connected to said second exhaust duct and an outlet connected to said series of heat exchangers adjacent sai'd second Zone, said subsequent zones and said last Zone and discharging to the atmosphere, heating burners disposed in said last named outlet between said blower and the first heat exchanger, a second catalytic vapor incinerator disposed in said last named outlet between said last named burners and the first heat exchanger, a third duct connecting said second Zone and the first heat exchanger, a second circulating fan having an inlet connected to the first heat exchanger and an outlet connected to said second plenum chamber, subsequent plenum chambers communicating with said subsequent zones and a last plenum chamber communicating with said last zone, said subsequent and last zones being connected through subsequent and last ducts to the heat exchangers adjacent to said subsequent and last zones, circulating fans for said subsequent and last zones having inlets connected to the heat exchangers adjacent said subsequent and last Zones and outlet connected to the plenum chambers in said subsequent and last zones and the entrance end to the exit end, a plurality of heat treating zones spaced longitudinally of said heat treating chamber including a first Zone adjacent said entrance end, a second zone following said rst Zone, subsequent zones following said second zone with a last zone adjacent said exit end, a plenum chamber communicating with said first zone for directing heated gases over coated articles, an open Vapor exhaust duct in said first Zone spaced inwardly of said entrance end, heating burners in said duct for heating gases passing therethrough from said first zone, a catalytic vapor incinerator disposed in said duct following the burners, a circulating fan having an inlet connected to said duct following said incinerator and an outlet connected to said plenum chamber, and an infiltration air by-pass conduit having an inlet opening adjacent the entrance end of said heat treating chamber and a discharge opening into said duct between said incinerator and the inlet to said fan, a second plenum chamber communicating with said second zone for directing heated gases over coated articles, a second open vapor exhaust duct communicating with said second Zone, a series of heat exchangers, a blower having an inlet connected to said second exhaust duct and an outlet connected to said series of heat exchangers adjacent said second zone, said subsequent zone and said last zone discharging to the atmosphere, heating burners disposed in said outlet between said blower and the first heat exchanger, a second catalytic vapor incinerator disposed in said last named outlet between said last named burners and the lirst heat exchanger, a third duct connecting said second zone and the iirst heat exchanger, a second circulating fan having an inlet connected to the first heat exchanger and an outlet connected to said second plenum chamber, subsequent plenum chambers communicating with said subsequent zones and a last plenum chamber communicating with said last zone, said subsequent and last zones being connected through said subsequent and last ducts to the heat exchangers adjacent said subsequent and last zones, circulating fans for said subsequent and last Zones having inlets connected to the heat exchangers adjacent said subsequent and last zones and outlets connected to the plenum chambers in said subsequent and last zones and a damper controlled fresh air inlet connected to the heat exchanger adjacent said last zone.

10. A coating oven for heat treating coated articles to evaporate coating solvents and remove combustibles from the vaporized solvents, said oven comprising an elongated heat treating chamber, having an entrance at one end and an exit at the other, means for conveying coated articles to be heat treated through said chamber from the entrance end to the exit end, a plurality of heat treating zones spaced longitudinally of said heat treating chamber including a iirst zone adjacent said entrance end, a second zone following said tiret zone, subsequent zones following said second zone with a last zone adjacent said exit end, a plenum chamber com-V municating with said iirst zone for directing heated gases over coated articles, a vapor exhaust duct in said irst zone, heating burners in said duct for heating gases passing therethrough from said irst zone, a catalytic vapor incinerator disposed in said duct following said burners, a circulating fan having an inlet connected to said duct following said incinerator and an outlet connected to said phenum chamber, a second plenum chamber communieating lwith said second zone for directing heated gases over coated articles, a second vapor exhaust duct communicating with said second Zone, a series of heat exchangers, a blower having an inlet connected to said second exhaust duct and an outlet connected to said series of heat exchangers adjacent said second zone, said subsequent zones and said last zone and discharging to the atmosphere, heating burners disposed in said last named duct between said blower and the first heat exchanger, a second catalytic vapor incinerator disposed in said last named outlet between said last named burners and the first heat exchanger, -a third duct connecting said second Zone and the rst heat exchanger, a second circulating fan having an inlet connected to the first heat exchanger and an outlet connected to said second plenum chamber, subsequent plenum chambers commuicating with said subsequent zones and a last plenum chamber communicating with said last zone, said subsequent and last zones being connected through subsequent and last ducts through the heat exchangers adjacent subsequent and last Zones, circulating fans for said subsequent and last zones having inlets connected to the heat exchangers adjacent said subsequent and last zones and outlets connected to the plenum chambers in said subsequent and last zones and a fresh air inlet connected to the heat exchanger adjacent said last zone.

ll. A coating oven for heat treating articles to evaporate coating solvent and remove combustibles from the vaporized solvents, said oven comprising an elongated heat treating chamber having an entrance at one end and an exit at the other, means for conveying coated articles to be heat treated through said chamber and from the entrance end to the exit end, a plurality of heat treating zones spaced longitudinally of said heat treating chamber including a iirst zone adjacent said entrance end, a second zone following said first zone, subsequent zones following said lsecond zone with a last zone adjacent said exit end, a plenum chamber communicating with said tirst zone for directing heated gases over coated articles,

a vapor exhaust duct in said first zone, heating burners in said duct for heating gases passing therethrough from said irst zone, a catalytic vapor incinerator disposed in said duct following said burners, a circulating fan having an inlet connected to said duct following said incinerator and an outlet connected to said plenum chamber, a second plenum chamber communicating with said second zone for directing heated gases over coated articles, a second vapor exhaust duct communicating with said second zone, a series of heat exchangers, a blower having an inlet connecting with said second exhaust duct and an outlet connected to said series of heat exchangers and discharging to the atmosphere heating burners disposed in said last named outlet between said blower and the iirst heat exchanger, a second catalytic vapor incinerator disposed in said last named outlet between said last named burners and the first heat exchanger, a third duct connecting said second zone and the rst heat exchanger, a second circulating fan having an inlet connected to the first heat exchanger and an outlet connected to said second plenum chamber, subsequent plenum chambers communicating with said subsequent zones and a last plenum chamber communicating with said last Zone, said subsequent and last zones being connected through subsequent and last ducts to the heat exchangers associated with said subsequent and last zones, circulating fans for said subsequent and last zones having inlets connected to the heat exchangers associated with said subsequent and last zones and outletsv connected to the plenum chambers in said subsequent and last zones and a fresh air inlet connected to the heat exchanger associated with said last zone.

References Cited in the iile of this patent UNITED STATES PATENTS 

